1. Field of the Invention
While the subject invention has utility in any sheet feeding system, it relates primarily to corrugated blank feeding equipment utilized in the corrugated paper industry wherein blanks are stacked and must subsequently be fed to processing equipment such as folding, cutting, creasing, and coating machines.
More particularly, the subject invention relates to feeding equipment wherein the lowermost blank is advanced from beneath the stack as contrasted to top sheet feeding which is utilized in some systems.
2. Prior Art
The prior art discloses many systems for feeding blanks which have featured various ways to apply suction to prevent the warped edges of advancing blanks from causing jam ups which result in machine down time. Standard feed beds of the type disclosed in U.S. Pat. No. 3,754,752 have utilized a perforated base plate to enable the suction to be applied to the lowermost blank to flatten warped or curled blanks during advancement.
In addition to the perforated plate type of structure, elongated rib-like vacuum chambers have also been used for the purposes of "flattening" or holding down warped blanks. Of detrimental consequence in both of these systems is the creation of friction between the blank and the table surface which must be overcome by the kicker device or other means used to advance the boards to the processing machinery. If the vacuum is too strong, inordinate friction is created between the advancing blank and the feed table surface requiring extreme force from the kicker device to push the sheets into the processing machinery where they are normally received by feed rolls. If the vacuum is relieved, then the front edge of the advancing blank may lift off the table causing jam ups, particularly if the blank is warped somewhat. In most standard processing machinery in the corrugated box industry, gates are positioned adjacent the feed rolls to prevent more than one blank from being fed to the processing machine simultaneously. It is against these gates that jam ups will occur when the vacuum is not sufficient to prevent the curling up of edges of warped board.
Additional types of suction assist devices have been utilized such as disclosed in U.S. Pat. No. 3,391,926 in which a top feeding system is disclosed. A suction chamber is utilized in combination with power driven wheels to enable the uppermost sheet to be driven by the wheels in the direction of the working machine where the sheet is fed onto a conveying belt or other means. The suction is not utilized to flatten warped board but rather, has the obvious purpose of enabling the uppermost board to be drawn into contact with the rotating wheels so that the board may be driven laterally by the wheels.
Powered wheels have also been used in combination with suction for alignment purposes as disclosed in U.S. Pat. No. 3,677,537. In this case, the wheels or friction rollers 20 are axially disposed in the direction of the advancing sheet. The purpose of the friction rollers 20 is to power drive the sheet that is to be advanced by feeder bar 32 to the desired alignment position against side guide structure 36.
Despite many different utilizations of suction assist techniques in the sheet feeding state of the art, the efficiency of all systems in use today leaves much to be desired. While generally, the most efficient way of advancing sheets has been the utilization of feed or kicker bar means, there has been lacking an effective way of supporting the advancing sheets whereby curling up of warped board and the like can be flattened while at the same time, the use of extreme suction, which serves to diminish the effectiveness of the feeding unit, can be avoided.